The European Union on Monday urged Myanmar to protect journalists from "intimidation, arrest or prosecution" after several cases of reporters running into trouble with the law, including three detained by the army last week.

The three reporters were accused of breaching the colonial-era Unlawful Associations Act after covering the burning of drugs by the rebel Ta'ang National Liberation Army to mark International Day Against Drug Abuse.

Journalists and rights groups say that over a year since democracy champion Aung San Suu Kyi's National League for Democracy came to power, the gains made in press freedom since the end of decades of strict military rule risk being reversed.

The European Union said the right to freedom of opinion and expression is a human right guaranteed to all.

"It constitutes one of the essential foundations of a democratic society," it said in a statement.

"We therefore call on the government of Myanmar to provide the necessary legal protection for journalists to work in a free and enabling environment without fear of intimidation, arrest or prosecution."

The three reporters arrested last week - Democratic Voice of Burma reporters Aye Nai and Pyae Phone Naing, and Lawi Weng of the Irrawaddy magazine - are in prison in the northeastern town of Hsipaw. The first hearing in their case is on July 11.

Suu Kyi's spokesman, Zaw Htay, has said that everyone "should be treated according to the law".

Suu Kyi herself has not commented on the three or on other cases of reporters running afoul of the law. Suu Kyi's defenders say the Nobel Peace Prize winner – who spent years under house arrest for opposing army rule – is hamstrung by a military-drafted constitution that keeps the generals in politics and free from civilian oversight.

The military said the three reporters had communicated with a group "currently opposing the country's rule of law using arms".

The European Union said that in recent months the arrest and prosecution of journalists had reached "a worrying number".

Most of the cases against journalists are for suspected violations of a broadly worded telecommunications law decried by human rights monitors as a violation of free speech.

In one such case, Kyaw Min Swe, an editor at the Voice daily, was arrested last month over an article mocking the military. His trial is underway.

Reporters protesting against what they see as the threat to press freedom say that military intelligence agents have taken their pictures, a reminder of the days of harsh military rule when no opposition was tolerated.